Electrochromic Windows Research Articles

Conjugated Polymers for Photo-electrochromic Devices

It is clear that the new generation smart windows will develop much more in the coming yearsand in this sense, new multifunctional materials will be used in this field. While the easy use of suchapplications makes people happy, on the other hand, it also highlights energy efficient housing andtransportation for humanity. There are some interesting parameters such as the control of daylight enteringor leaving smart windows, self-power supply, and display functionality. Among the various chromogeniccolor changes, electrochromic methods are the fastest and easiest to control. Electrochromic materials arehigh-performance materials that are preferred both in the scientific world and in technological devices withtheir interesting electrochemical and optical properties. These materials can be inorganic or organic based,such as transition metal oxides, viologen systems and conductive polymers. Among them, electrochromicconductive polymers attract more attention with their superior mechanical, electrochemical and opticalproperties in portable electronics. Moreover, the ease and low cost of the synthesis procedures, as well asits low power and performance superiority, further solidify its rise among other materials in this sense. Bymodifying the chemical structures of conductive electrochromic polymers (or monomers) as desired, sharpand vivid color changes can be observed even at room temperature. The development of new electrochromicpolymers can be with various modifications of the main chain, as well as side chain engineering,morphology control. Electrochromic properties of thin films of conductive polymers polymerized bychemical or electrochemical methods can be used in photo-electrochromic applications for informationstorage and various imaging purposes. In this study, it is desired to give information about conjugatedpolymers for self-powered electrochromic windows.

ProDOT-Based Polymers: From Energy Storage to Smart Window Applications

Nowadays, electroactive materials based on conjugated polymers for energy storage and electrochromic window applications attract large interest due to their low cost, accessible synthetic procedures, and interesting electrochemical properties. Herein, we report on the performance of two propylenedioxythiophene (ProDOT)-based polymers having varying length and functionality side chains, which were explored to assess their potential for these applications. The polymers were obtained by oxidative chemical polymerization and processed from organic solvents into thin coatings with different molecular assemblies. Preliminary studies on their chemical structure and optical and electrochemical characteristics were performed to evidence how these are influenced by the side chain substituent nature. When tested as electrode material in the three-electrode cell configuration, the synthesized ProDOT-based polymers provided the highest specific areal capacitance of 1.059 mF/cm2 at a scan rate of 10 mV/s and 0.538 mF/cm2 at 0.01 mA/cm2 in cyclic voltammetry and galvanostatic charge–discharge measurements, respectively. One of the polymers showed electrochromic response, with ultrafast color change from deep purple to highly transmissive green/blue. A coloration efficiency of 123 cm2/C and a maximum CE decay of 9.9% after 100 cycles was achieved for this material, which is also able to efficiently store electrical charge, thus demonstrating potential for use in energy storage smart window applications where the energy level can be estimated by simple visual observation.

Experimental investigation on indoor thermal environment improvement and energy-saving of electrochromic window under Singapore's tropical climate

This study aims at analyzing the thermal performance improvement of a gray tintable electrochromic window (EC window) under Singapore's tropical climate. Two climate chambers were experimentally studied, one with a double-glazed EC window and another with a single-glazing window, the most common in the considered region, as the reference. The indoor thermal environment and air conditioning energy consumption were compared respectively to investigate the thermal performance improvement of the EC window. The results, under the sunny outdoor weather condition, showed that the EC window could achieve an interior surface temperature reduction of 4.4 °C under the tinted state and 3.0 °C under the clear state, compared to the reference window. Moreover, the bleached EC window achieved up to 37% improvement in peak Predicted Mean Vote (PMV) over the reference window, while the fully tinted EC window achieved a 50% improvement in peak PMV. Finally, the EC window under the fully tinted state could achieve up to 19% energy savings compared to the reference window. Using the EC window under Singapore's tropical climate can improve the occupant thermal comfort during the daytime and reduce air conditioning energy consumption.

Study on the impact of photovoltaic electrochromic modular smart window on indoor environment

Both electrochromic window (EC) and photovoltaic (PV) shading technology can control the indoor lighting environment. However, their combination form has great impact on the performance. The innovative smart windows with photovoltaic electrochromic (PV-EC) modules are designed, and consisted with photovoltaic areas, EC areas and transparent areas. Because the position of different modules can be adjusted freely, the system can select the most suitable combination mode for different building applied conditions. The PV-EC modular smart window test rig was established to learn the influence of different combinations of the windows on lighting condition. The combination(d) has the largest useful daylighting illumination among them, and which reaches 75.26%. PV area is installed at the lower layer, EC area is installed at the middle layer, and transparent area is installed at the upper layer in combination (d). Compared with ordinary windows, the window system can save up to 15.79% energy. And for different floors, radiation areas and space types, the system can select the corresponding combinations to adjust the lighting environment. It shows that the window system could improve the lighting environment and energy saving of the building, and effectively copes with different building condition.

Selective Electrochromic Regulation for Near-Infrared and Visible Light via Porous Tungsten Oxide Films with Core/Shell Architecture.

Dual-band electrochromic smart windows have become a research hotspot owing to their unique ability to selectively control near-infrared (NIR) and visible (VIS) light. However, the design and exploitation of dual-band electrochromic films are still an extreme challenge due to the scarcity of relevant high-performance materials. To solve this issue, we here proposed a type of porous WO3 film with nanowires/nanoparticles core/shell architecture as a promising candidate, endowing smart windows with a dual-band electrochromic feature. Moreover, the mechanism of the dual-band electrochromism is illustrated by the response of the transmittance spectra in Li+-based or TBA+-based electrolytes to distinguish the electrochemical behavior and the cyclic voltammetry to determine the degree of diffusion-limited kinetics. Our results indicate that the dual-band electrochromic performance is credited to the progressive electrochemical reduction procedure, in which the capacitive charging process gives rise to NIR regulation and the following ion intercalation contributes to VIS light modulation. Furthermore, we develop a dual-band electrochromic energy storage prototype device utilizing the porous WO3 film. This work describes a judicious strategy for designing dual-band electrochromic films, promoting the evolution of dual-band electrochromic technology.

Porous WO3·2H2O film with large optical modulation and high coloration efficiency for electrochromic smart window

Porous WO3·2H2O film with large optical modulation and high coloration efficiency for electrochromic smart window

Controlling crystallinity of oxygen-deficient tungsten oxide on SnO2 nanoflake arrays for advanced dual-band electrochromic smart window

Controlling crystallinity of oxygen-deficient tungsten oxide on SnO2 nanoflake arrays for advanced dual-band electrochromic smart window

Flexible Electrochromic Device on Polycarbonate Substrate with PEDOT:PSS and Color-Neutral TiO2 as Ion Storage Layer.

Electrochromic (EC) windows on glass for thermal and glare protection in buildings, often referred to as smart (dimmable) windows, are commercially available, along with rearview mirrors or windows in aircraft cabins. Plastic-based applications, such as ski goggles, visors and car windows, that require lightweight, three-dimensional (3D) geometry and high-throughput manufacturing are still under development. To produce such EC devices (ECDs), a flexible EC film could be integrated into a back injection molding process, where the films are processed into compact 3D geometries in a single automized step at a low processing time. Polycarbonate (PC) as a substrate is a lightweight and robust alternative to glass due to its outstanding optical and mechanical properties. In this study, an EC film on a PC substrate was fabricated and characterized for the first time. To achieve a highly transmissive and colorless bright state, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) was used as the working electrode, while titanium dioxide (TiO2) was used as the counter electrode material. They were deposited onto ITO-coated PC films using dip- and slot-die coating, respectively. The electrodes were optically and electrochemically characterized. An ECD with a polyurethane containing gel electrolyte was investigated with regard to optical properties, switching speed and cycling behavior. The ECD exhibits a color-neutral and highly transmissive bright state with a visible light transmittance of 74% and a bluish-colored state of 64%, a fast switching speed (7 s/4 s for bleaching/coloring) and a moderately stable cycling behavior over 500 cycles with a decrease in transmittance change from 10%to 7%.

Integrated Thermoelectric Design Inspired by Ionic Liquid Microemulsion-Based Gel with Regulatable Dual-Temperature Responsiveness

The concept and principles of chromatic engineering of electrolytes have demonstrated charming prospects for constructing pluralistic electrochromic devices. Here, we develop a synthetic design bearing thermochromic and electrochromic behaviors based on the ionic liquid (IL) microemulsion-based gel, driven by the intrinsic thermodynamic stability of microemulsion and ionic conductivity of IL. The prepared gel can tune light-scattering behaviors as the droplet expanded or aggregated when the temperature is out of its thermodynamically stable temperature range. Not only that, oil-phase IL ([EMIM]TFSI) as well as introduced LiCl and LiTFSI endows it with satisfactory ionic conductivity, making it able to be utilized as a free-standing electrolyte layer for the electrochromic smart window. Therefore, the fabricated smart window based on this gel and WO3 electrochromic layer successfully realizes dual-stimuli responsiveness for both temperature and electric field, possessing energy-saving combined with privacy protection function. In addition, the component compatibility of microemulsion allows the harmonious introduction of hydrophilic antifreeze moisturizer ethylene glycol (EG) and hydrophobic ultraviolet absorber 2-hydroxy-4-(octyloxy)benzophenone (2H4MBP), which further promotes the multifunctional integration of a smart window for the strengthened safety factor, anti-freezing, anti-drying, and anti-UV capabilities. Finally, we extend the application of the IL microemulsion-based gel to an ionic writing plate based on the same electrochromic mechanism. In brief, this innovative preparation method paves the way for multifunctional electrochromic devices.

Unveiling the Multistep Electrochemical Desorption Mechanism of Cubic NiO Films for Transmissive-to-Black Electrochromic Energy Storage Devices.

Electrochromic smart windows offer dynamic control of sunshine and solar heat in modern architecture. Yet, how to obtain aesthetically pleasing color tuning states such as gray and black is a great challenge, and the corresponding desorption mechanism in electrochromism is still not well understood. Here, we report one transmissive-to-black NiO electrochromic film assembled by a facile and low-cost electrostatic spray technology, which achieves ultralarge optical modulation, high coloration efficiency, and remarkable energy storage capacity. By in-depth experimental analyses and the first-principle calculations, multistep electrochemical desorption mechanisms of OH- and electrochromic switching kinetics of the NiO film were unveiled. Additionally, the assembled NiO film-based smart energy storage indicator can visually display its energy storage level in real time. Our obtained NiO films and subsequent devices can serve as potential candidates in a broad range of innovative electrochromic applications including multifunctional smart windows, energy-efficient displays, energy-storage indicators, electronic labels, etc.

Developing an IoT-based electrochromic windows for smart buildings

ABSTRACT Different solutions have been investigated to reduce energy consumption in buildings in recent years. The use of smart windows to change the solar irradiation entering the building and to reject the solar heat has been one of these approaches. An IoT-based smart electrochromic window was created for this study, and both its technical stability and functionality were assessed in a laboratory environment. For six cities in different climate classes in Iran in 2019, simulations revealed that the indoor horizontal illuminance had a higher priority than the temperature in controlling the transparency of the windows during the first six months of the year. And it resulted in an average reduction of about 45% in the energy used for lighting and cooling in a medium-sized building. Additionally, the proposed window's energy efficiency varied according to climate, with arid climates having the highest efficiency and continental climates having the lowest. HIGHLIGHTS IoT-based Smart Electrochromic Window. Control algorithms for smart electrochromic windows. Simulation of the energy consumption in buildings.

Study of the Correlation among Luminous Properties of Smart Glazing for Adaptive Energy Saving Buildings

A smart window, such as electrochromic or thermochromic windows, may not be able to accomplish at the same time energy efficiency and visual comfort functions, since satisfying one criterium interferes with the other. This recalls to the important issue of establishing precise relationships among parameters affecting energy, glare control, and color rendering tasks and the influence on them of glazing material composition and preparation technique. With this aim, the luminous properties of a number of advanced glazings found in literature and of three home-made electrochromic devices differing by material composition and/or preparation technique are analyzed in this study. The investigation has involved the determination of the CIE (Commission International de l’Eclairage) Color Rendering Index (CIE CRI), the Correlated Color Temperature (CCT), and the luminous transmittance coefficient (τV) of the devices which are discussed with regard to their potential in absolving to energy and visual comfort tasks. Results lead to the main conclusion that the CIE CRI, CCT, and τV indexes are clearly linked by an exponential correlation. At low τV values (τV< 0.5), however, the correlation weakens and the variation of the CIE CRI and CCT indexes becomes entirely material dependent. The influence of preparation technique appears to be irrelevant since the color rendering indexes appear to be well correlated to τV over all the investigated τV range.

Thin Polymer Films by Oxidative or Reductive Electropolymerization and Their Application in Electrochromic Windows and Thin-Film Sensors.

Electrically conducting and semiconducting polymers represent a special and still very attractive class of functional chromophores, especially due to their unique optical and electronic properties and their broad device application potential. They are potentially suitable as materials for several applications of high future relevance, for example flexible photovoltaic modules, components of displays/screens and batteries, electrochromic windows, or photocatalysts. Therefore, their synthesis and structure elucidation are still intensely investigated. This article will demonstrate the very fruitful interplay of current electropolymerization research and its exploitation for science education issues. Experiments involving the synthesis of conducting polymers and their assembly into functional devices can be used to teach basic chemical and physical principles as well as to motivate students for an innovative and interdisciplinary field of chemistry.

Review on Mechanoresponsive Smart Windows: Structures and Driving Modes.

The growing awareness about the global energy crisis and extreme weather from global warming drives the development of smart windows market. Compared to conventional electrochromic, photochromic, or thermochromic smart windows, mechanoresponsive smart windows present advantages of simple construction, low cost, and excellent stability. In this review, we summarize recent developments in mechanoresponsive smart windows with a focus on the structures and properties. We outline the categories and discuss the advantages and disadvantages. Especially, we also summarize six unconventional driving modes to generate mechanical strain, including pneumatic, optical, thermal, electric, magnetic, and humidity modes. Lastly, we provide practical recommendations in prospects for future development. This review aims to provide a useful reference for the design of novel mechanoresponsive smart windows and accelerate their practical applications.

An Electrochromic Nickel Phosphate Film for Large-Area Smart Window with Ultra-Large Optical Modulation

HighlightsTransition metal phosphates were first developed for the electrochromic application.The obtained NiHPO4·3H2O film achieves an ultra-large optical modulation of 90.8%, and the electrochromic mechanism is systematically elucidated using in situ and ex situ techniques.A large-area electrochromic smart window with 100 cm2 is constructed, which displays superior performances in regulating natural lighting and storing electrical charges.

Tungsten-oxide/polypyrrole film for hybrid solid-state electrochromic smart window

An organic–inorganic hybrid electrochromic device was fabricated by combining the films of hydrothermally synthesized tungsten oxide (WO3) with electrodeposited polypyrrole. Before making a device, these deposited thin films were characterized using scanning electron microscopy, infrared spectroscopy, and Raman spectroscopy techniques. Thereafter, a solid-state organic–inorganic electrochromic device was fabricated, which shows reversible switching between coloration and bleaching states with a very small external bias voltage (±1 V) and excellent cyclic stability up to 500 s with a negligible amount of transmission loss. In situ electrochemical studies show that the device has enhanced switching speed (1.1/1.8 s), and optical contrast of more than 47% at the wavelength of 650 nm. Furthermore, the optimized electrochromic device displays enhanced coloration efficiency up to ∼304 cm2/C. All these results open a new door for increasing the performance of a single-layered device by combining it with complementary electrodes.

A Low Driving-Voltage Hybrid-Electrolyte Electrochromic Window with Only Ferreous Redox Couples.

Even after decades of development, the widespread application of electrochromic windows (ECW) is still seriously restricted by their high price and inadequate performance associated with structural/fabrication complexity and electrochemical instability. Herein, a simple hybrid electrochromic system based on PFSA (perfluorosulfonic acid)-coated Prussian blue (PB, Fe4III [FeII(CN)6]3) film and Ferricyanide-Ferrocyanide ([Fe(CN)6]4-/[Fe(CN)6]3-)-containing hybrid electrolyte is reported. The PB film and the [Fe(CN)6]4-/[Fe(CN)6]3- couple show near redox potentials well inside the electrochemical window of water, resulting in a low driven voltage (0.4 V for coloring and -0.6 V for bleaching) and a relatively long lifespan (300 cycles with 76.9% transmittance contrast retained). The PFSA layer, as a cation-exchange structure, significantly improves the transmittance modulation amplitude (ΔT: 23.3% vs. 71.9% at a wavelength of 633 nm) and optical memory abilities (ΔT retention: 10.1% vs. 67.0% after 300 s open-circuit rest increases) of the device, by means of preventing the direct contact and charge transfer between the PB film and the [Fe(CN)6]4-/[Fe(CN)6]3- couple. This "hybrid electrolyte + electron barrier layer" design provides an effective way for the construction of simple structured electrochromic devices.

A layer-stacked NiO nanowire/nanosheet homostructure for electrochromic smart windows with ultra-large optical modulation.

The structural engineering of active materials at the nanoscale level is crucial to improving the performance of electrochromic devices. However, an insufficient structural design inevitably results in limited electron/ion transportation and inadequate electrochromic performance. Herein, a new type of layer-stacked nanowire/nanosheet homostructure is proposed for enhancing the electrochromic properties of transition metal oxide films. Benefiting from the one-pot feature integration of nanowire and nanosheet structures, the NiO film with a unique homostructure delivers ultra-large optical modulation up to 93.4% at 550 nm and a high coloration efficiency of 72.1 cm2 C-1 in comparison with NiO-based materials. In addition, the film maintains 91% of its optical modulation over 1000 cycles of coloration and bleaching processes. Furthermore, the high performance of the device was verified by integrating the NiO film with the TiO2 ion storage layer in assembled smart windows with a dual function of electrochromic and energy storage. As a proof of concept, the integration of solar cells with electrochromic devices demonstrates the great significance of self-powered smart windows for energy-saving. To this end, such a strategy of structural design for electrochromic films would offer a distinctive pathway toward studying high-performance electrochromic systems.

Oxygen vacancy modulated amorphous tungsten oxide films for fast-switching and ultra-stable dual-band electrochromic energy storage smart windows.

Dual-band electrochromic energy storage (DEES) windows, which are capable of selectively controlling visible (VIS) and near-infrared (NIR) light transmittance, have attracted research attention as energy-saving devices that integrate electrochromic (EC) and energy storage functions. However, there are few EC materials with spectrally selective modulation. Herein, oxygen vacancy modulated amorphous tungsten oxide (a-WO3-x-OV) is firstly shown to be a potential material for DEES windows. Furthermore, experimental results and density functional theory (DFT) calculations demonstrate that an oxygen vacancy not only enables the a-WO3-x-OV films to modulate NIR light transmittance selectively, but also enhances ion adsorption and diffusion in the a-WO3-x host to obtain excellent EC performance and a large energy storage capacity. Consequently, the a-WO3-x-OV film can selectively control VIS and NIR light transmittance with a state-of-the-art EC performance, including high optical modulation (91.8% and 80.3% at 633 and 1100 nm, respectively), an unprecedentedly fast switching speed (tb/tc = 4.1/5.3 s), high coloration efficiency (167.96 cm2 C-1), high specific capacitance (314 F g-1 at 0.5 A g-1), and ultra-robust cycling stability (83.3% optical modulation retention after 8000 cycles). The fast-switching and ultra-stable dual-band EC properties with efficient energy recycling are also successfully demonstrated in a DEES prototype. The results demonstrate that the a-WO3-x-OV films show great potential for application in high-performance DEES smart windows.

Robust and stable dual-band electrochromic smart window with multicolor tunability.

Dual-band electrochromic smart windows (DESWs) can selectively control the transmittance of near-infrared (NIR) and visible (VIS) light, which can significantly reduce building energy consumption. However, almost all the reported DESW colors switch between clear colorless and dark blue. The single color combined with the dazzling visual experience of blue will undoubtedly limit the application scene of DESWs. Herein, for the first time, we report a robust and stable DESW with multicolor conversion capabilities based on the single-component organic polymer polyaniline (PANI). The results show that the progressive electrochemical reaction enabled PANI film to deliver not only efficient and independent control of NIR and VIS light transmittance but also impressive electrochromic performance-rich color conversion (yellow-green-black), good optical modulation (65% at 633 nm and 59% at 1600 nm), high coloration efficiency (367.1 cm2 C-1 at 633 nm and 299.6 cm2 C-1 at 1600 nm), and excellent cycling stability (optical modulation losses of 6% at 633 nm, and 4% at 1600 nm after 10 000 cycles). Thereby, we demonstrated a prototype PANI-based DESW device (10 × 5 cm2), which delivered a multicolor electrochromism together with independent control and modulation of the VIS (sunlight) and NIR (solar heat) transmittance.